Aspects and embodiments of the invention pertain to optical display systems. Particular embodiments pertain to augmented reality systems that include a controllable optical image-generating apparatus and an optical image-viewing apparatus, associated methods, and applications thereof and to virtual reality systems that include a controllable optical image display/view apparatus, associated methods, and applications thereof. More particularly, aspects and embodiments of the invention pertain to optical display systems, and associated methods, in which a display (viewable) pixels can be offset by a portion of a pixel width. Applications include but are not limited to wearable display devices including virtual and/or augmented reality devices.
Virtual reality is an emerging wearable display technology for applications including but not limited to immersive video games and interactive three-dimensional (3D) graphics. A critical issue with these types of display devices is the low image resolution. Due to the high angular resolution of human eye (˜1 arcminute), when a display panel is magnified with a lens, as in cases of virtual reality headsets such as HTC Vive, Google cardboard/daydream or Oculus Rift, the pixel resolution of a 2160×1200 panel can only provide an angular resolution of ˜5.5 arcmin (for each eye). Even when the display panel is improved to 4320×2400, the resolution is improved to ˜2.75 arcmin. In order to achieve the high angular resolution of human eye (˜1 arcminute), the minimal required resolution would be 11880×6600.
Another possible approach to enhance resolution and thus the user experience without altering the display panel is to produce an offset to the display pixels in time domain, such as in U.S. Pat. Nos. 5,369,266 and 6,243,055 B1, where one or more birefringent crystal plates are used to produce an offset for different polarized light to create an offset of half pixel. At least a polarization rotator is needed to switch between two polarization states. Through time-multiplexing (i.e., display an image for the first frame, and an offset image for the second, offset frame), an effectively doubled-resolution display can be obtained.
U.S. Pat. No. 5,689,283 discloses an optical device based on the same time-multiplexing concept. In this device, the pixel offset is realized through a rotating prism-array. A similar design is disclosed in US Patent 2004/0041784 A1.
However, the abovementioned devices and associated methods are only suitable for projection systems, where the form-factor is not critical. They are impractical for the requirements of compact, head-mounted displays.
More recently, a super-resolution display was proposed in [F. Heide, D. Lanman, D. Reddy, J. Kautz, K. Pulli, D. Luebke, “Cascaded Displays: Spatiotemporal Superresolution using Offset Pixel Layers,” ACM Transactions on Graphics, Vol. 33, No. 4, Article 60, (2014)] by stacking LCD panels with offset pixels. Although the device is relatively compact, significant light loss is inevitable due to the low transmittance of LCD panels.
The inventors have thus recognized the advantages and benefits of an image resolution enhancement apparatus and method that is optically and mechanically simpler, lighter, less expensive, and better performing than what is currently available.